Numerical value controller

Abstract

A numerical value controller for a machine tool includes a storage unit storing a machining program for drilling a hole in a workpiece in accordance with relative movement between a tool and workpiece in a depth direction, and a control unit controlling the relative movement between the tool and workpiece based on the machining program and that moves the tool relative to the workpiece in the depth direction from a return point to a hole bottom point. The return point is a position retracted in the depth direction from a workpiece surface where the tool starts to perform drilling. The machining program includes a command for a workpiece height point as a position of the workpiece surface. The control unit moves the tool relative to the workpiece in the depth direction at a relative rate higher than a cutting feed rate from the return point to the height point.

The invention claimed is: 
     
       1. A numerical value controller for a machine tool, the numerical value controller comprising:
 a memory that stores a machining program for drilling a hole in a workpiece in accordance with relative movement between a tool and the workpiece in a depth direction extending along a longitudinal axis of the tool; and 
 a processor configured to control the relative movement between the tool and the workpiece based on the machining program and move the tool relative to the workpiece in the depth direction from a return point to a hole bottom point, 
 wherein the return point is a position retracted in the depth direction from a workpiece surface where the tool starts to perform a drilling process, 
 wherein the machining program includes a command for a workpiece height point serving as a position of the workpiece surface in the depth direction, 
 wherein the processor is configured to: 
 move, from the return point to an intermediate position between the return point and the workpiece height point, the tool relative to the workpiece in the depth direction at a rapid traverse rate higher than a cutting feed rate; and 
 change, at the intermediate position, a relative rate of the tool relative to the work piece in the depth direction from the rapid traverse rate to the cutting feed rate, and 
 wherein the intermediate position is determined according to a responsiveness of mechanical control of the machine tool. 
 
     
     
       2. The numerical value controller according to  claim 1 , wherein the workpiece height point is a numerical value stored in the numerical value controller. 
     
     
       3. The numerical value controller according to  claim 1 ,
 wherein the machining program causes the machine tool to execute a plurality of canned cycles each including a positioning operation, a drilling operation, and a removing operation, 
 wherein the positioning operation involves positioning a drilling position of the workpiece relative to the tool by moving the tool and the workpiece relative to each other in a direction intersecting the depth direction, 
 wherein the drilling operation involves drilling a hole in the drilling position by moving the tool in the depth direction from the return point to the hole bottom point, 
 wherein the removing operation involves removing the tool from the hole by moving the tool in the depth direction from the hole bottom point to the return point, and 
 wherein the processor is configured to: 
 start the drilling operation before the positioning operation ends, to relatively move the tool along a first curved path from the return point to the workpiece height point; and 
 start the positioning operation in a subsequent canned cycle before the removing operation ends, to relatively move the tool along a second curved path from the workpiece height point to the return point. 
 
     
     
       4. The numerical value controller according to  claim 1 , wherein, in step drilling involving reciprocating the tool a plurality of times in the depth direction to drill a hole by a predetermined amount every time until the hole reaches the hole bottom point, the processor is configured to retract the tool to the workpiece height point or to a height between the return point and the workpiece height point.